Low elongation synthetic rope



Dec. 19, 1967 C ANN 3,358,434

LOW ELONGATION SYNTHETIC ROPE Filed July is. 1965- INVENTOR. FRANK C.McCA /v \crw'nsmd iioumsnmi A TTORNEYS United States Patent 3,358,434LGW ELGNGATION SYNTHETIC RSPE Frank C. McCann, Grange, Calif., assignorto Tuhbs Cordage Company, San Francisco, Calif. Filed July 16, 1965,Ser. No. 472,574 9 Claims. (Cl. 57-444) ABSTRACT OF THE DISCLOSURE Asynthetic polyolefin rope formed from twisted polyolefin yarn and acentral core of pre-stretched polyester fiber. The presence of thepolyester fiber in minor amounts, i.e., up to about 25% by weight,provides the rope with low elongation properties similar to thatobtained with rope formed entirely of polyester fiber.

This invention relates to synthetic rope. More specifically, it pertainsto rope made from a novel combination of filaments of at least two typesof thermoplastic synthetic resin, one type being a polyolefin and theother type being a polyester, with the resultant product beingcharacterized by its low elongation properties.

A number of thermoplastic synthetic fibers, possessing a wide variety ofproperties, have been developed. Certain polyolefin filaments, such aspolypropylene, have the advantage and properties of high resistance tochemical and biological degradation, heat resistance, and dielectricstrength. Their use is sometimes limited by their relatively highelongation.

On the ohter hand, suitably prepared polyester filaments, such as Mylar(trademark of Du Pont for polyester of diethylene glycol andterephthalic acid), have been found to possess high strength and verylow elongation as well as the other advantages of synthetic fibers.Unfortunately, these filaments are quite costly and therefore not alwayssuited for use in ropes where a large cross-sectional dimension isnecessary. Such a rope might have a tensile strength greatly in excessof that required. The excess of structural properties would in effect bewasted in the attempt to provide a given cross-sectional dimension.

The present invention provides an all synthetic rope that can beeconomically manufactured to have the desired larger cross-sectionaldimensions. This is achieved through the predominate use of therelatively inexpensive polyolefin fibers, such as polypropylene. Whileusing these polyolefin fibers the product of the invention eliminatesthe undesired elongation of polyolefins through combination with arelatively minor amount of pre-stretched polyester threads in thestrands of the rope as will be discussed more fully hereinafter.

The rope of this invention has low dielectric properties together withthe chemical resistance of synthetics. The rope is economically feasiblefor use where cost is a limiting factor and Where the cross-sectionaldimensions of the rope are critical, such as in the cases where the ropeis to be hand grasped, i.e. certain aspects of sailing and in otherspecial cases such as in rope operated extension ladders. These usesrequire low elongation which is not found in polyolefins previouslyavailable but which requirement is satisfied by the present ropes.

Aside from the cross-sectional dimensions or bulk, another advantageover pure polyester rope of the same 3,358,434 Patented Dec. 1%, 1967strength (which would have a small cross section) is found in an addedsafety feature. When the polyester content elongation is exceededcausing the polyester filaments to break, the large polyolefin contentof the rope is still available as a backstop. While the polyolefinfibers may elongate under the forces at work, these forces may not besufiicient to cause a break of the polyolefins entirely and thus willavoid a complete severance of the rope long enough to take correctiveaction.

In the accompanying drawings:

FIG. 1 is an elevation of a three strand rope constr-ucted in accordancewith the present invention;

FIG. 2 is a cross-section of the rope of FIG. 1 showing the relationshipof the polyolefin and polyester components thereof; and

FIG. 3 is a cross-section taken through an alternate embodiment of thepresent invention in which the rope is in braided form instead of thetwisted form of FIGS. 1 and 2.

In general, the present rope may be constructed with one or more strandstwisted together in conventional fashion. Each strand is formed with aplurality of twisted polyolefin yarns. Each strand also contains acentral core of pre-stretched polyester thread in an amount sufiicientto significantly decrease the elongation of the polyolefin yarns.

Alternatively, and as shown in FIG. 3, the invention may be utilized inthe fabrication of braided type rope in which one or more braided outercoverings of a polyolefin surrounds a core of parallel filaments. Atleast some of the filaments are pre-stretched polyester thread.

The term pre-stretched polyester thread as used in this specificationand claims includes those polymers formed by the condensation reactionof an alkylene glycol with a phthalic acid. The reaction between twosuch materials, e.g. ethylene glycol and terephthalic acid isillustrated by the following equation.

When this condensation reaction is catalytically accelerated, theresulting chain reaction produces a polyester of diethylene glycol andterephthalic acid. The polyester is generally obtained in a continuoustransparent, highly flexible film form. A number of commerciallyavailable polyester films which generally possess the properties desiredherein and are commercially available under such trademarks as thefollowing: Dacron, Kodel, Vycron and Fortrel. The material known asMylar is especially useful for present purposes. All of these materialsare polyesters of the above general type with minor variations developedby the proprietor of the trademark.

The polyester film as supplied by the manufacturer must be processed orpre-stretched into a thread form prior to use in the manufacture of theinstant ropes. In general, the polyester film is run between twocapstans under tension. At the same time, heat is applied to the film.The combination of heat and tension reduces the film to a threadconfiguration and substantially removes the elongation of the material.At this point the threads 3 are ready for incorporation in the presentropes. Polyester thread of this type is well-known in the art andcommercially available.

Polyolefin as used in this application is meant to include conventionalfilaments which are characterized by their relatively low elasticrecovery, low tensile strength and low density. Such filaments or yarnsgenerally have molecular weights less than about 100,000 and areextruded from such resin polymers as polyethylene and polypropylene.Polypropylene yarns are preferred for present purposes.

As noted above, the rope of this invention is made with differingamounts of the two types of synthetic resins. The polyolefin is thepredominate component of the rope with the polyester forming a centralcore along the longitudinal axis of the rope. In general, the resultsdesired are best achieved where the polyester core comprises about10-25% by weight of the two synthetics utilized in the rope, with thepolyolefin, therefore, running from about 7590% of the rope dependingupon the polyester content. A particularly advantageous rope has beenmade with polypropylene and Mylar polyester wherein the Mylarconstitutes about 15% by weight of the rope.

The strands for the rope may be made by conventional methods andmachines. In the preferred embodiment, a plurality of polyester threadsare utilized rather than one large single thread, and these threads aretwisted and inserted as a central core for helically wound outerpolyolefin yarns. In the preferred embodiment three strands are twistedin the usual fashion to form a rope with each strand having thepolyester core as noted. While the polyester could be intermixed withthe polyolefin, a significant advantage in the manufacture of the ropeis obtained through the use of the central core concept.

Referring to the drawings showing the preferred three strand rope, FIG.1 shows strands 1, 2 and 3 helically interwoven in conventional (regulartwist) configuration. The end of strand No. 1 is shown with its yarns 4,5 and 6 separated so that the central polyester core 7 is exposed.

In the cross-sectional view of FIG. 2 the relationship of the parts canbe more clearly seen. The three strands 1, 2 and 3 are similar and onlystrand 3 is illustrated in detail. Strand 3 is composed of polyolefinssuch as polypropylene yarns 4, 5 and 6 which are helically wound about acentral core 7, which constitutes the polyester threads. Polyesterthread 7 is a plurality of individual polyester threads which take on ahelical twist during manufacture of the rope.

In the alternate embodiment shown in FIG. 3, a braided rope isillustrated. The rope contains an outer covering 8 made from apolyolefin, such as polypropylene, and in which the filaments areintertwined in conventional braid configuration. The outer covering maybe made in a plu rality of layers if desired. The central core 9 isformed with a plurality of relatively straight parallel longitudinalfilaments. The bulk of the filaments may be made of any suitablematerial and will generally be a polyolefin similar to that used informing the outer covering 8. The central core also contains a pluralityof pre-stretched polyester threads 10 to provide the low elongationproperties of the rope.

The rope illustrated in FIG. 3 will generally exhibit less elongationthan the twisted rope illustrated in FIGS. 1 and 2. The central corefilaments of the braid are actually shorter in a given length of rope ascompared with the length of polyester thread found in the same length oftwisted rope. In the twisted rope the center filaments are longer sincethey define a helix along the rope, whereas the center filaments of thebraid are relatively straight and parallel. As a result, when theelongation forces are applied to the rope of this invention, a certainamount of untvvisting of the filaments in the twisted rope must occurbefore the central polyester thread becomes loaded. The elongation whichoccurs during this untwisting move- Ineut is avoided in the braid ropesince the polyester 4 thread is immediately stressed when elongationforces are applied.

The rope obtained from the above constructions can be made to have theequivalent strength of naturally occurring fiber rope together withdesirable bulk at a reasonably low cost. At the same time, the new ropeof this invention eliminates the elongation properties of the previouslyknown low cost synthetics and retains the usual properties of syntheticsuch as chemical resistance and resistance to biological degradation aswell as the desirable dielectric properties.

While a good deal of variation in proportions is possible depending uponthe requirements for the rope end product the following figures willdemonstrate the advantageous properties of the present invention. Thus,a diameter, 3 strand polypropylene (regular twist) rope is made upcontaining 15% by weight pre-stretched Mylar polyester. The polyesterwas inserted as a twisted central core for each of the strands of thepolypropylene. This rope had an elongation of 1.8% under a 200 lb. load.The same size rope made entirely from polypropylene has an elongation of5% under the same load making it unacceptable for many uses.

' Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it is understood that certain changes and modificationsmay be practiced within the spirit of the invention as limited only bythe scope of the appended claims. 7

What is claimed is:

1. An improved synthetic polyolefin rope characterized.

by low elongation properties comprising: at least one strand formed froma plurality of twisted polyolefin yarns and a central core for saidstrand of pre-stretched polyester thread in an amount sufiicient tosignificantly decrease the elongation of said polyolefin yarns.

2. A synthetic rope in accordance with claim 1 wherein said central corecomprises a plurality of twisted polyester threads, and said polyolefinis selected from the group consisting of polypropylene and polyethylene.

3. A synthetic rope in accordance with claim 2 wherein said polyolefinis polypropylene.

4. A synthetic rope in accordance with claim 1 wherein said strandcontains about 10-25% by weight of polyester thread.

5. A synthetic, two-component, fibrous rope comprising: three helicallywound strands, each strand composed of a central core constituting about15% by weight of the strand of twisted prestretched Mylar polyesterthreads, and an outer covering for each of said strands of a pluralityof twisted and helically wound polypropylene yarns.

6. An improved low elongation rope formed from at least two differentsynthetic resin comprising: a plurality of helically wound strands, eachof said strands composed of an outer covering formed from a plurality oftwisted and helically wound yarns of polyolefin selected from the groupconsisting of polypropylene and polyethylene, and

a central core for each of said strands, constituting about.

1025% by Weight thereof, of polyester threads formed from polyester filmthat has been drawn into thread form under heat and tension.

7. An improved synthetic polyolefin rope characterized by low elongationproperties comprising: an outer cover formed from a plurality ofpolyolefin yarns and a central core for said outer cover, including asuflicient amount of pre-stretched polyester thread to significantlydecrease the elongation of the polyolefin yarns.

8. A synthetic rope in accordance with claim 7 wherein said polyolefinis selected from the group consisting of polypropylene and polyethylene.

9. A synthetic braided rope of low elongation comprising: a plurality ofparallel elongate polyolefin yarns, a plurality of pro-stretchedpolyester threads mixed with said polyolefin yarns and parallel thereto,and a braided 5 6 covering for said polyolefin yarns and polyesterthreads FOREIGN PATENTS formed from polyolefin y 585,066 10/1959 Canada.

811,501 4/1959 Great Britain.

References Cited 996,874 6/1965 Great Britain.

UNITED STATES PATENTS 5 891,618 9/1959 Great Britain. 2 v gigg; 28 73FRANK I. COHEN, Primary Examiner. 3,205,649 9/ 1965 Nishet et al.5-7-140 DONALD E. WATKINS, Assistant Examiner.

3,315,455 4/1967 Stoller 57144

1. AN IMPROVED SYNTHETIC POLYOLEFIN ROPE CHARACTERIZED BY LOW ELONGATIONPROPERTIES COMPRISING: AT LEAST ONE STRAND FORMED FROM A PLURALITY OFTWISTED POLYOLEFIN YARNS AND A CENTRAL CORE FOR SAID STRAND OFPRE-STRETCHED POLYESTER THREAD IN AN AMOUNT SUFFICIENT TO SIGNIFICANTLYDECREASE THE ELONGATION OF SAID POLYOLEFIN YARNS.